Discharge lamp colors are the result of particular atomic emissions and are adjustable by selecting different chemical compositions, and gas pressures. Possible lamp colors are then determined by the limited number of useful gases, and phosphors, where a phosphor is used. Mercury is a strong emitter of ultraviolet light and is commonly used in lamps to gain the full range of available phosphor colors. Unfortunately, mercury is limited by its range of useful operating temperatures. There are also environmental concerns about its use. Without mercury, the number of useful phosphors is reduced, and so is the number of colors that may be efficiently produced. There is a particular need for an efficient mercury free discharge lamp in combination with the proper method of operation that will generate white light.
Phosphors can have differing emissions, and efficiencies depending in part on their firing and dopants. The similar compositions, or the same composition if processed differently can give differing results. Phosphors do not respond to the shorter neon UV emissions in the same way they respond to the longer mercury UV emissions. Phosphor response to neon emission therefore cannot be determined by looking at phosphor response tables generated for mercury emissions. Also the shorter neon emissions do not pass through a glass or quartz lamp, so the phosphors cannot be tested on the exterior of a generic neon lamp. The phosphor must be inside the lamp to generate the correct response. These factors make phosphor selection and testing for use in a neon lamp inherently difficult.